Generic depth indicator for surgical navigational tools

ABSTRACT

A depth-indicating device for determining the depth of insertion of a surgical tool comprising a pair of spaced apart end caps, separated by a compressed spring, with the surgical tool passing through axial openings in both end caps, and firmly attached to one of the end caps, but free to slide through the opening in the other. A guide tube is attached to the second endcap, such that the surgical tool can be guided to its operating position on a body part. The second end cap and guide tube are attached to a location having a known position relative to the body part. A tracking marker is attached to the first end cap such that its longitudinal position can be tracked using a remote racking camera. Since the surgical tool is attached to the first end cap, the tool position is also tracked by the tracking system.

FIELD OF THE INVENTION

The present invention relates to the field of devices used in surgicalnavigation, especially minimally invasive procedures, for use indetermining the insertion depth of a surgical tool.

BACKGROUND OF THE INVENTION

Depth indication is an important part of surgical navigation capability,allowing for the user to observe and be alerted to the current real-timedepth of a surgical trajectory in comparison to patient anatomicallandmarks. This capability is necessary especially in procedures inwhich the surgeon is operating under video-guided or other forms ofindirect vision, to prevent as much as possible, depth-related errors.In minimally invasive procedures, the ability to accurately determinethe depth of a surgical tool is important because of the practicalinability to properly assess distance in a three dimensional scenario,without a proper line of sight. Errors in depth can easily causeirreversible disability or fatality, for example, in spinal procedures,by accidental insertion of sharp tools and implants beyond the vertebraeinto the spinal cord or aorta.

A number of prior art navigational devices exist. Amongst such devices,U.S. Pat. No. 5,409,493 to Greenberg for “Single-handed Surgical DrillDepth Guide” discloses a device, specifically for treating fractures inthe cranio-maxillofacial region. The depth gauge is used to determinethe correct screw length during a fixation procedure. U.S. Pat. No.7,165,336 to Kim for “Surgical Depth Instrument” describes a device formeasuring the depth of a hole in a bone having a digital readout forproviding measurements to the operator. Both of these devices arehandheld tools with specific and limited uses. WO 2015/112566 filed byConformis Inc., for “Spring-fit Surgical Guides” describes ablock-shaped spring-fit tool guide that may include depth detection,designed to assist in tool alignment during joint implant procedures.U.S. Pat. No. 9,198,698 to Doose et al. for “Minimally Invasive SpinalFixation System and Related Methods” discloses a minimally invasivespinal fixation system with guides and instruments for aiding ininsertion and positioning of rods during a spinal fixation operation.

U.S. Pat. No. 5,732,703 to Kalfas et al. for “Stereotaxy Wand and TooGuide” discloses a device connected to a navigation system. The systemcomprises a series of light emitters on the wand that are detected by aset of CCD camera receivers. A calibration procedure is required toalign the wand with the remote detection system, after which the wand,in combination with a tool guide, can be used to plan a tool trajectory.The wand-tool guide component of the system is designed to be handheldby the operator.

Several problems exist with current navigational devices, leaving thefield with a need for a solution that rectifies these deficiencies. Oneproblem is the need for calibration. With some surgical navigationsystems, every tool must be individually calibrated before each use. Notonly is this technical verification process time-consuming—it is alsoprone to human error. A second difficulty is that in many prior artsystems, a positional marker is attached to the tool and viewed by anassociated navigation system. If the marker moves out of view of thecamera because the tool was rotated by the operator or positioned behindanother object, the tool will lose connection with the remote navigationsystem and thus cease to preserve its relative position, thereby losingits ability to indicate depth. Finally, with current surgical navigationsystems, the process of tool calibration is generally limited todesignated tools compatible with a given navigation system. A surgeonusing a certain navigation system may prefer or need to use a tool of adifferent company with different or incompatible navigation markers, oreven may wish or need to use a tool that is not compatible with anymarker at all.

Therefore, there exists a need for an intra-operative depth indicatorand tool guide which overcomes at least some of the disadvantages ofprior art systems and methods.

The disclosures of each of the publications mentioned in this sectionand in other sections of the specification, are hereby incorporated byreference, each in its entirety.

SUMMARY

The present disclosure describes a new exemplary generic intra-operativedepth indicator device for determining the depth of insertion of asurgical tool, that is not limited to a specific navigation or trackingsystem or to a specific manufacturer and which requires nopre-calibration when used on a platform such as a surgical robotic arm,or a fixed mounting position.

The device comprises three basic components—a pair of spaced apart endcaps, conveniently in the form of thin plate-like elements, which arekept separated by a compressed spring. The surgical tool passes throughaxial openings in both end caps, and is firmly attached to a first oneof the end caps, but free to slide through the opening in the second. Aguide tube is advantageously attached to the second end cap, such thatthe surgical tool passing through the opening in the second end cap canbe accurately guided to its operating position on a body part. Thissecond end cap and guide tube are attached to a location having a knownposition relative to the body part. A tracking marker is attached to thefirst end cap such that its longitudinal position relative to the secondcap fixed to the location having a known position relative to the bodypart, can be tracked using a remote navigation or tracking camera, aspart of a navigation or tracking system. Since the surgical tool isfirmly attached to the first end cap, the tool position relative to thebody part is also tracked by the tracking system, and hence also theoperating end of the tool, whose depth of entry into the body part, thedevice it is intended to monitor. The tracking marker is mounted on arotating arm, allowing the marker to rotate freely in 360 degrees aroundthe device axis, such that a clear tracking line of sight can beobtained regardless of obstructions generated during the surgicalprocedure.

There is therefore provided according to a first exemplaryimplementation of the devices described in this disclosure, a device fordetermining the depth of insertion of a surgical tool, the system,comprising:

(i) a first and a second cap element, each cap having an axial openingadapted for insertion of the surgical tool, the surgical tool beingfixed in the axial opening in the first cap element and freely movablethrough the opening in the second cap element,

(ii) a compressed spring extending between the first and second capelements,

(iii) a tool guide attached to the second cap element, and

(iv) a first position marker attached to the first cap element, suchthat the position of the first cap element can be determined in a remotetracking system,

wherein the second cap element is disposed at a location whose spatialposition is known.

In such a depth-indicating device, the location may be the end effectorof a robotic arm. In such a case, the position of the end effector ofthe robotic should be correlated with the remote tracking system, suchthat the depth indicating device provides a correct indication of theposition of the tool taking into account any motion of the end effector.

Alternatively, the location may be a fixed support in the region of abody part on which the surgical tool is to operate. The spatial locationof a body part on which the surgical tool is to operate may be known tothe remote tracking system.

Any of the above described devices may further comprise a secondposition marker attached to the second cap element, or to a componenthaving a known spatial relation to the second cap element, such that thespatial position of the second cap element can be determined in theremote tracking system.

Furthermore, in any of the above described devices the first positionmarker may be attached to the first cap element, such that it can freelyrotate about the axis of the cap element, such that if the line of sightbetween the first position marker and the remote tracking system isobstructed, the first position marker can be rotated to a differentorientation, and the position of the first cap element can be determinedusing aid first position marker in the different orientation.

Additionally, in such devices the spring may have a free length suchthat it remains compressed when the first and the second cap elementsare separated by their maximum intended distance. Also, the spatialposition of the location may be known to the tracking system.

Finally, according to any of the previously described depth-indicatingdevices, the spatial position of the location may be known relative tothe body part on which the surgical tool is to operate by means of theremote tracking system and a marker element mounted in a known locationrelative to the anatomical body part. As an alternative, the spatialposition of the location may be known relative to the body part on whichthe surgical tool is to operate by means of a registration procedureinvolving anatomical comparisons using intraoperative images.

The terms tracking and navigation, are used interchangeably in thepresent application, and are understood to mean the ability to determinethe pose (position and orientation) of an object being tracked ornavigated.

BRIEF DESCRIPTION OF THE DRAWINGS

The presently claimed invention will be understood and appreciated morefully from the following detailed description, taken in conjunction withthe drawings in which:

FIG. 1 shows a schematic view of an implementation of the inventionusing the generic spring depth control navigation device to measure thedepth of entry of a surgical drill bit into a vertebral body; and

FIG. 2 shows details of the depth indicator in operation and itsconnection to a robotic arm

DETAILED DESCRIPTION

Reference is now made to FIG. 1, which illustrates schematically oneexample of the generic depth indicator of the present disclosure. Aspring 1 is contained between end caps 3, 4 by each of its ends. Theunloaded length of the spring must be greater than the maximum distancebetween the end caps 3, 4, in order to always maintain the spring in aminimally compressed state end, such that the end caps 3, 4, are alwaysat a clearly defined distance apart, for any normal mutual position ofthe end caps. The proximal end cap 3, contains an opening 7 into which asurgical tool 9 can be inserted and attached to the end cap 3, such thatthe cap moves with motion of the tool, or vice versa. The term proximalis used throughout this disclosure to relate to that end of an elementcloser to the operator, while the term distal relates to the end closerto the subject. To the proximal cap is attached a navigation marker 2,which can optionally rotate around the axis of the device through 360degrees. The function of this marker will be described hereinbelow. Thedistal cap 4 also has an opening 17, through which the surgical tool 9can freely slide, and this cap acts as an anchoring cap in that it isattached or anchored to a position whose location in space is definedrelative to the anatomic body part on which the tool is to operate. Thisposition could be either a fixed position, or the end effector of arobotic arm 6, whose position in space relative to the anatomic elementis defined by the robotic control. The pose of the end effector of therobotic arm should be known relative to the subject's anatomy—in theexample shown, a spinal vertebra 10—by any of the methods known in theart, whether by means of three dimensional navigation markers, or byusing a registration procedure for defining the pose of the robotic armrelative to the bone using intraoperative images.

In addition, a tool guide 8 is also attached to the fixed referenceposition, or the end effector of the robotic arm 6, together with theanchor cap 4, such that the surgical tool 9 passes through the opening17 in the anchoring cap 4, and down the tool guide 8, as is known in theart. The tool guide may have a serrated distal end (not shown) forgripping a bone onto which it is aligned, to prevent skiving. The endcaps 3, 4, and the spring 1 together comprise a depth indicator 14. Thesurgical tool 9 is inserted through the depth indicator 14, which isattached to the fixed reference position or to the robotic arm 6 fromabove, and through the tool guide 8 which is also attached to the fixedreference position or the robotic arm 6.

Actuation of the depth indicator occurs when the surgical tool 9, a bonedrill in the exemplary implementation shown in FIG. 1, is advanced bythe surgeon. Since the surgical tool is firmly clamped to the end cap 3,longitudinal motion of the surgical tool 9 results in correspondinglongitudinal motion of the end cap 3, thereby compressing the spring 1of the depth indicator 14 between the proximal end cap 3 and the distalend cap 4, which is held in the robotic arm. The spring may bephysically connected to the end caps 3, 4, or simply retainedtherebetween by the compression of the spring. The position of theproximal end cap 3 is monitored by means of a navigation system, whichcan determine the position of a marker element 2 attached to the endcap. A navigational tracking camera 13 is shown remotely positioned in alocation where it can surveille the operating region, and determine thethree dimensional position and orientation of any navigation markers inthe surveillance region. The displacement of the marker element 2relative to the fixed location of the distal end cap 4, is measured bythe navigation system. That displacement can alternatively be determinedby means of one or more additional marker elements 5 attached in a fixedposition relative to the distal end cap 4, whose position can bedetermined by the same navigation system 13 as that used to determinethe position of the proximal, moving end cap 3. The depth indicator isthus able to determine the linear longitudinal displacement of thesurgical tool 9 affixed to the proximal ends cap 3, and hence, from aknowledge of the starting point of the end tip of the tool, thedisplacement of that end tip as the surgeon proceeds with the insertionprocedure.

Reference is now made to FIG. 2, which is a schematic close-up view ofthe depth indicator 14. A surgical tool 9 is shown inserted through theopening 7 in the distal cap 3 of the device, to which it is firmlyattached. The surgical tool 9 extends through the spring 1, the opening7 in the proximal cap 4, and the tool guide 8, which is attached to thefixed reference position, or to the robotic arm 6. The fixed referenceposition, or the position of the robotic arm used for holding the depthindicator at its distal end cap, may be equipped with navigationalmarkers 5, such that their location is known to the navigation system.As the surgical tool 9 is advanced by the surgeon into the bone, theproximal end cap 3 also moves distally with the drill, thus compressingthe spring in a linear direction 12, and this distal linear movement ofthe markers 2 attached to the end cap is detected by the navigationsystem, which can thus provide a measure of the distal movement of thetool tip.

Since navigation markers 2 may be obscured by the device as the linearlongitudinal motion 12 proceeds, or as the surgeon moves his hands, themarker may be attached to the proximal endcap in a manner that allows itto rotate 11 around the axis of the device, such that if one particularposition shields the navigational line of sight, the marker may berotated until visual line of sight contact is again made with thenavigation system detector camera 13. In the example shown in FIG. 2,the marker element 2 is attached by means of an arm 14 to a rotarybearing (not shown) attached to the axis of the device at the end plate3, such that the marker element can rotate freely around the deviceaxis, and at a known distance D therefrom. The marker 2, has athree-dimensional layout, whose configuration is known. Thatconfiguration defines a known axis, and a known plane of the marker. Inthe example marker shown in FIG. 2, the marker element has a linear formwhose length axis is perpendicular to the plane of rotation of themarker element around the axis of the depth indicator, and hence isparallel to the axis of the tool, and a fixed distance D away therefrom.The navigational system to able to determine, from the three dimensionalconfiguration of the marker element, its angular rotational positionrelative to the alignment of the depth indicator, and its distance fromthe axis is known, such that the longitudinal position of the tool canbe determined regardless of the rotational position of the marker. Thus,the marker can be freely rotated to avoid obstruction of the line ofsight, and still is able to track the longitudinal insertion of thetool.

When use is made of a tool not having angular symmetry, there is a needto relate the rotational position of the tool with the depth indicator,such that the orientational detection mode of the navigation system canrelate to the correct orientation of the tool as the marker is swungaround the tool axis. This can be achieved by providing a directionalindication in the end plate or another part of the depth indicator, suchas a longitudinal slot, which interfaces with a matching feature on thetool, such that the tool orientation is known to the navigational systemand to the angular position of the rotating marker.

The described device has advantages over prior art devices. First,having its own navigation markers operable through 360 degrees, enablesit to be fully functional for depth detection in any position. Further,as the device is independent of need for calibration, it saves time andeliminates the error range incumbent in human-dependent procedures. Itcan be used with any robotic arm or navigation system. The device isdesigned to be used in combination with a fixed tool guide and does notneed to be removed or exchanged with the tool guide in order to operatethe tool.

It is appreciated by persons skilled in the art that the presentinvention is not limited by what has been particularly shown anddescribed hereinabove. Rather the scope of the present inventionincludes both combinations and subcombinations of various featuresdescribed hereinabove as well as variations and modifications theretowhich would occur to a person of skill in the art upon reading the abovedescription and which are not in the prior art.

1. A depth-indicating device for determining the depth of insertion of asurgical tool, the system, comprising: a first and a second element,each element having an axial opening adapted for insertion of thesurgical tool, such that, after insertion, the surgical tool is fixed inthe axial opening in the first element and freely movable through theopening in the second element; a compressible spring extending betweenthe first and second elements; a tool guide attached to the second capelement; and a first position marker attached to the first element, suchthat the position of the first element can be determined in a trackingsystem remote from the depth-indicating device; wherein the secondelement is configured to be disposed at a location whose spatialposition is known to a robotic system or to the remote tracking system.2. A depth-indicating device according to claim 1, wherein the secondelement is attached to the end effector of the robotic system.
 3. Adepth-indicating device according to claim 2, wherein the position ofthe end effector of the robotic system is correlated with the remotetracking system, such that the depth indicating device provides anindication of the pose of the tool taking into account any motion of theend effector.
 4. A depth-indicating device according to claim 1, whereinthe second element is attached to a fixed support in the region of abody part on which the surgical tool is to operate.
 5. Adepth-indicating device according to claim 1, wherein the spatiallocation of a body part on which the surgical tool is to operate isknown to the remote tracking system.
 6. A depth-indicating deviceaccording to claim 1, further comprising a second position markerattached to the second element or to a component having a known spatialrelation to the second element, such that the spatial position of thesecond element can be determined in the remote tracking system.
 7. Adepth-indicating device according to claim 1, wherein the first positionmarker is attached to the first element such that it can freely rotateabout the axis of the first element, such that if the line of sightbetween the first position marker and the remote tracking system isobstructed, the first position marker can be rotated to a differentorientation, and the pose of the first element can be determined usingthe first position marker in the different orientation.
 8. Adepth-indicating device according to claim 1, wherein the first andsecond elements have a maximum separation distance and wherein thespring has a free length such that it remains compressed when the firstand the second elements are separated by the maximum separationdistance.
 9. A depth-indicating device according to claim 1, wherein thespatial position of the second element is known to the remote trackingsystem.
 10. A depth-indicating device according to claim 1, wherein thepose of the second element is known relative to the body part on whichthe surgical tool is to operate, by the remote tracking system and amarker element mounted in a known location relative to the anatomicalbody part.
 11. A depth-indicating device according to claim 1, whereinthe pose of the second element is known relative to the body part onwhich the surgical tool is to operate by a registration procedureinvolving anatomical comparisons using intraoperative images.
 12. Atracking device for a surgical arm having an end effector, the trackingdevice comprising: a first depth detector member configured to securelyengage a first portion of a surgical tool passing through the endeffector of the surgical arm, the first depth detector including atracker configured to provide location information to a remote trackingsystem; a second depth detector member configured to slidingly engage asecond portion of the surgical tool, the second depth detector memberbeing configured to be secured at a fixed location relative to the endeffector of the surgical arm; and a resilient member extending betweenthe first and second elements.
 13. The tracking device of claim 12,further comprising a tool guide attached to the second depth detectormember.
 14. The tracking device of claim 12, wherein a pose of thesecond depth detector member is known relative to a body part on whichthe surgical tool is to operate, by the remote tracking system and amarker element mounted in a known location relative to the body part.15. The tracking device of claim 12, wherein a pose of the seconddetector member is known relative to a body part on which the surgicaltool is to operate by a registration procedure involving anatomicalcomparisons using intraoperative images.
 16. The tracking device ofclaim 12, wherein the tracker is configured to selectively rotate aboutan axis of the first depth detector member, such that if the line ofsight between the tracker and the remote tracking system is obstructed,the tracker can rotate to a different orientation and a pose of thefirst depth detector member can be determined using the tracker in thedifferent orientation.
 17. A tracking device for a surgical systemhaving an end effector, the tracking device comprising: a first depthdetector member configured to securely engage a first portion of asurgical tool, the first depth detector including a tracker configuredto provide location information to a remote tracking system; a seconddepth detector member configured to slidingly engage a second portion ofthe surgical tool, the second depth detector member being configured tobe disposed at a location whose spatial position is known relative to abody part on which the surgical tool is to operate; and a resilientmember extending between the first and second elements.